Battery system

ABSTRACT

A battery system for use in a vehicle is disclosed having a first battery for selectively powering the motor to start the engine, and having a first voltage level and a charge level. The system includes a second battery to operate and maintain the accessory electrical loads, and having a second voltage level. The system includes a charging switch coupling the first battery to the alternator. The system also includes a charge maintenance device coupling the first battery to the second battery to maintain the charge level of the first battery to a predefined magnitude in response to a control signal. The system also includes a controller coupled to both the first battery and the second battery to monitor the first voltage level and the second voltage level, and operating the charging switch and the charge maintenance device in response to the first voltage level and the second voltage level.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a division of U.S. patent application Ser.No. 09/204,207, titled “Advanced Battery Controller with State of ChargeControl” filed Dec. 2, 1998, which is hereby incorporated by reference.The present application claims the benefit of U.S. ProvisionalApplication Serial No. 60/074,629 filed Feb. 13, 1998, which is herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to battery powered electricalsystems, such as in motor vehicles; and more particularly to a controlsystem for monitoring and maintaining the charge of the battery whilethe electrical system is in an inactive state.

BACKGROUND OF THE INVENTION

Automobiles and other combustion engine powered vehicles typicallyemploy an electric motor to start the combustion engine. For thatpurpose, the electric motor is coupled to a starting circuit whichgenerally receives electrical power from an on-board storage battery.The starting circuit selectively couples electrical energy from thebattery to the starting motor that operates to cycle the engine toinitiate sustained operation. In common vehicle applications, thebattery also provides electrical energy to a variety of electric powerconsuming devices, such as engine control electronics, lights, andvehicle accessories.

Traditional batteries for these applications, often referred to asstarting, lighting and ignition (SLI) batteries, are multi-cell,lead-acid batteries. That is, the batteries are constructed from leadplates pasted with active material and arranged into stacks. Thosestacks are inserted into partitioned cell compartments of a batterycontainer, electrically interconnected, and flooded with dilute acidelectrolyte. SLI batteries of this construction are more than adequatefor providing the relatively high power demand required of enginestarting, as well as the relatively low power demand to maintainelectrical accessories during both vehicle operation and periods ofnon-operation. However, because of the seemingly disparate functions theSLI battery is required to perform, short duration high-power output andlong duration low-power output, the battery design can not be optimizedfor performing either of these tasks. An additional drawback of thesebatteries is relatively low specific energy (kilowatt hour/gram, kWh/g)as compared to other battery constructions owing to the weight of thelead plates and the liquid electrolyte.

There has been suggested a battery system for vehicle use which includestwo batteries. A first battery in the system, a starting battery, isoptimized to start the engine by being specifically designed for shortduration, high-power output. A second battery in the system, a reservebattery, is optimized to operate and maintain non-starting electricalloads, such as for vehicle accessories. An advantage of such a system isthat the starting battery may be made smaller and lighter yet capable ofproviding a high power output for a short period of time. In addition,the reserve battery may be made smaller and lighter yet capable ofsatisfying the relatively low power requirements of vehicle accessories.In combination, the two batteries may require less space and weigh lessthan a single traditional SLI battery.

A limitation of a two battery system lies with maintaining the charge ofboth batteries. Typically, the vehicle includes a voltage/currentregulation device which regulates the output of the alternator inresponse to the charging needs of the SLI battery and the vehicleelectrical loads. In the dual battery system, each battery type deliverspower and accepts charge at a different r ate. For example, the startingbattery delivers power at a very high rate and likewise accepts chargeat a high rate. In contrast, the reserve battery delivers power at alower rate and accepts charge at a lower rate. Moreover, it willtypically be the case that each battery will be at a differentstate-of-charge, hence requiring different charge maintenance.Additional advantages may also be attained by selectively coupling ordecoupling the batteries during inactive, starting and operationalperiods of the vehicle. However, careful management is required so asnot to damage either the vehicle electrical system or the dualbatteries.

Another problem encountered with battery powered equipment is batterydrain during periods of inactivity. For example, a motor vehicle may sitparked for several weeks or months. In that situation a leakage currentor current drawn by accessories left turned-on can drain the battery toa point where the remaining charge is insufficient to start the engine.Thus it is desirable to provide a control mechanism that responds to aperiod of inactivity by disconnecting non-essential loads from thebattery.

SUMMARY OF THE INVENTION

The present battery system is particularly adapted for use in a vehiclewhich has an electric motor for starting an engine, an alternator drivenby an engine to generate electricity, and accessory electrical loads Thebattery system has a first battery for selectively powering the electricmotor to start the engine and a second battery to operate and maintainaccessory electrical loads. A charge maintenance device connects thefirst battery to the second battery for the purpose of maintaining thecharge of the first battery at a predefined level. A controller monitorsthe voltage level of the first battery to sense when the battery chargelevel has decreased to a level at which recharging is needed. At thattime the controller operates the charge maintenance device to rechargethe first battery from the second battery.

In the preferred embodiment of the battery system a charging switch isprovided which selectively connects the first battery to the alternator.The controller activates the charging switch in response to voltageacross the second battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing incorporation of the present inventioninto a dual battery electrical system of a motor vehicle; and

FIG. 2 is a block schematic diagram of the circuitry for the chargemaintenance device shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described in terms of a preferred embodimentadapted for use in a dual-battery based vehicle electrical system. Thebatteries in the system provide electrical energy for various vehicleoperation functions and receive charging from the vehicle electricalsystem. It will be appreciated that the scope of the invention is notlimited to vehicle applications or dual battery systems. For example,the invention may find application in a single battery system.

In various preferred embodiments of the present invention, batterycontrol electronics, vehicle control electronics and combinations of thethese electronic control devices are utilized for battery chargemanagement and enhanced system performance. For example, the system isadaptable to automatically determine charge status of the batteries inthe system and to couple, as appropriate, the battery or batteries withsufficient charge to operate essential vehicle electrical loads and toprovide energy for starting. In addition, a preferred charge managementstrategy reduces the potential for over-charging one or more of thesystem batteries and yet maintains each of the batteries at a readystate-of-charge. The control system also disconnects non-essential loadsfrom the batteries when the battery voltage drops below a defined levelduring periods of vehicle inactivity. These and other advantages andfeatures of the present invention will be appreciated from thedescription of the preferred embodiment which follows.

Referring to FIG. 1, a vehicle electrical system 10 includes a batterysubsystem which has a starting battery 14 coupled for providingelectrical energy to engine starting motor 22 through starter relaycontacts 24. Starting motor 22 is mechanically coupled to the engine ofthe vehicle (not shown) for starting the engine as is well known in theart. Starting battery 14 is preferably a high-rate battery, such as theone shown and described in commonly assigned U.S. patent applicationSer. No. 08/870,803 entitled: “Modular Electric Storage Battery” filedJun. 6, 1997, now U.S. Pat. No. 6,265,091, the disclosure of which ishereby expressly incorporated herein by reference.

A reserve battery 20, which is preferably an absorptive glass mat (AGM)type construction with a high reserve capacity, is adapted to provide arelative low-rate discharge for an extended period of time. The reservebattery 20 furnishes power to essential vehicle electrical loads 15.

The electrical system 10 also includes system controller 18 coupled toboth starting battery 14 and the reserve battery 20. The controller 18is a microcomputer with internal memory and input/output ports andexecutes a control program to perform the functions being describedherein. Controller 18 governs the connection of the starting battery 14and the reserve battery 20 to electrical system 10, and particularly tothe essential vehicle loads 15 and other vehicle loads 30, forselectively providing electrical energy during normal vehicle operationand during inactive periods. The essential vehicle loads 15 may comprisesuch devices as the vehicle engine/power train controller, safety systemcontroller and the like which require power even during periods when thevehicle is not operating. Non-essential vehicle loads 30 may includeaccessories such as interior lights, entertainment systems, conveniencefeatures and the like, which are not required to be powered duringinactive periods.

An alternator 21 also is connected to electrical system 10. Thealternator is mechanically driven by the engine in a manner that is wellknown in the art and during periods of vehicle operation generateselectrical energy for charging starting battery 14 and reserve battery20 under the supervision of controller 18. The alternator 21, pursuantto operation of controller 18, also provides electrical energy tovehicle loads 15 and 30, as well as ignition system 32 during normaloperation. The output of alternator 21 is controlled through fieldvoltage regulation or other suitable means responsive to the controller18 or the engine/power train controller (not shown) as is known in theart.

A charging switch, formed by contacts of relay 16, directly couple thestarting battery 14 and reserve battery 20. A charge maintenance device12, also referred to as a “charge pump”, is connected in parallel withthe relay contacts. The charge maintenance device 12 under control ofcontroller 18 couples energy from the reserve battery 20 to the startingbattery 14 to maintain the charge status of starting battery. Forexample, energy may be channeled to the starting battery 14 duringperiods when the vehicle is not being used or during periods ofoperation where the starting battery requires additional charge. Since arelatively small power draw from reserve battery 20 may be used tomaintain starting battery 14 at a substantially full state-of-chargewithout adversely effecting the charge status of reserve battery 20, theself-discharge characteristic of starting battery 14 may be overcome.

FIG. 2 illustrates a preferred embodiment of charge maintenance device12 having a circuit 200 which provides milliampere current pulses fromreserve battery 20 to starting battery 14. The circuit 200 includes NANDgates 202, 212 and 214 which are operatively coupled to form a pulsegenerator, specifically the reserve battery 20 is coupled a first inputof NAND gate 202 through transistor switch 238 which is operated by theenable signal (EN) from the controller 18. A second input is coupled tooutput of NAND gate 202 by resistor 204. A series combination ofresistor 208 and diode 206 is coupled in parallel with resistor 204 andcapacitor 210 couples the second input to circuit ground. The connectionof components forms a square wave oscillator. That is, when switch 236is closed, NAND gate 202 produces a periodic pulse train. The precisefrequency of the pulse train is not critical to operation of circuit200, but is preferably set at about 5-30 kilohertz (kHz).

The pulse train is buffered and amplified through NAND gates 212 and 214and coupled via a resistor network, including resistors 216 and 218, tothe gate of transistor 220. In the preferred embodiment, transistor 220is a field effect transistor (FET), but it should be understood that anysuitable switching device may be used without departing from the fairscope of the invention. The application of the pulse train alternatelyturns on and off transistor 220.

When transistor 220 is conductive, current flows from the positiveterminal 28 of reserve battery 20 through inductor 226, transistor 220and resistor 224. This causes voltage to build up across the inductor226. In the non-conductive state of transistor 220, the voltage built upacross inductor 226 is discharged through a current limiting resistor234 into the starting battery 14, thereby providing a charge maintenancecurrent. Diode 228 prevents reverse current flow, and resistor 230 andZener diode 236 provide a voltage dumping path which protects transistor220 from excessive voltage. Zener diode 236 preferably has a 15-16 voltreverse breakdown level thereby clamping the voltage across inductor 226at that level. Construction and operation of the charge maintenancedevice 12 is described in greater detail in commonly assigned U.S.patent application Ser. No. 08/1932,950 entitled “Battery ChargeMaintenance System and Method” filed Sep. 17, 1997 by a co-inventor ofthe present invention, now U.S. Pat. No. 6,222,341, and the disclosureof which is hereby expressly incorporated herein by reference.

When the alternator is not producing electricity, the controller 18 actsto open and close switch 238 for activating and deactivating the chargemaintenance circuit 200 to maintain the starting battery at a givencharge level. However, it is possible to allow circuit 200 to operatecontinuously without adverse affect to either starting battery 14 orreserve battery 20. Nevertheless, to maximize the standby capability ofthe system the preferred embodiment of circuit 200 is activated whenstarting battery 14 voltage falls below a predefined threshold, as willbe described subsequently. For example, the controller 18 sensesstarting battery 14 voltage and when it falls below approximately 12.75volts to close switch 238 activate the charge maintenance device 12.

Once activated, controller 18 initiates a timer, and the chargemaintenance device 12 is allowed to operate for 6 to 24 hours dependingcapacity of the starting battery 14 and the ability of circuit 200 toprovide charge current to starting battery 14. At the conclusion of thetime period, switch 238 is opened deactivating charge maintenance device12. Controller 18 also can be adapted to sense when starting batteryvoltage exceeds a threshold value for deactivating the chargemaintenance device 12, or the controller may continuously activatedevice 12 in response to various operating conditions, for example,environmental conditions such as extreme ambient cold.

Referring again to FIG. 1, during normal starting of the motor vehicleengine when the batteries 14 and 20 are properly charged, charging relay16 is de-energized so that the starter motor 22 is powered only by thestarting battery 14 when the starter relay contacts 24 close. At thistime, the controller 18 monitors the voltage across each battery 14 and20 via connections provided by conductors 23 and 25, respectively, tothe positive terminals of the batteries. If the controller 18 sensesthat the voltage from the reserve battery 20 is below a given levelduring starting, the controller energizes charging relay 16 so that thestarting battery 14 will be connected to supply power to those other carloads 15. In this normal condition, other car loads 15 are powered bythe reserve battery 20.

Once the engine starts, if the voltage provided to the car loads 15(i.e. the voltage at terminal 28) is 13.6 volts or more, the controller18 energizes charging relay 16 so that the starting battery 14 ischarged by voltage from alternator 21. However, when the voltageprovided to the car loads 15 drops to 13.1 volts or less, the chargingrelay 16 is de-energized so that its contacts open terminating chargingof the starting battery 14.

The controller 18 also provides protection against the batteriesbecoming excessively drained during periods when the motor vehicle isinactive. To this end, the non-essential accessory vehicle loads 30 areconnected to the positive terminal 28 of the reserve battery 20 througha first MOSFET transistor 34, and the ignition circuit 32 is coupled tothat positive terminal 28 through a second MOSFET transistor 36. Thegate electrodes of first and second MOSFET transistors 34 and 36 areconnected to and operated by separate outputs of controller 18, therebyacting as power switches which govern application of electricity to theaccessory vehicle loads 30 and the ignition circuit 32.

When the driver parks the motor vehicle, the controller 18 detects thatthe ignition switch 40 has been turned off and responds by activating aninternal timer. After a predefined period of time (e.g. two minutes)elapses, the controller 18 begins periodically measuring the voltageprovided by the reserve battery 20. Should that voltage drop below 12.2volts the controller 18 turns off the first MOSFET transistor 34 therebydisconnecting power from being applied yo non-essential accessory loads30. This stops further power consumption by such loads, as a dashboardclock, which otherwise would drain the reserve battery further. Thisdisconnection conserves the remaining battery charge.

Upon exiting the vehicle, the driver may press a button of a key fob 42of a type used in keyless entry systems. That action causes the fob 42to transmit a radio frequency (RF) signal 44 to a receiver 26 in thevehicle to indicate that the security system for the vehicle should bearmed. In response, the RF receiver 26 sends a security system armedsignal to the controller 18, which responds by turning off the secondMOSFET transistor 36 disconnecting application of electrical power tothe ignition circuit 32. This action prevents a car thief from beingable to start the car, even if the thief is able to operate the ignitionswitch 40.

Upon returning to the vehicle, the driver presses another button of thekey fob 42 which transmits a radio frequency (RF) signal indicating thatthe security system should be disarmed. The receipt of this second RFsignal is communicated by the receiver 26 to the controller 18 whichresponds by turning on both first and second MOSFET transistors 34 and36, thereby powering non-essential accessory loads 30 and the ignitioncircuit 32. Preferably, these loads and circuit remain activated for apredefined time interval (e.g. two to five minutes) as determined by atimer within the controller 18. If this time period elapses without theengine starting, the first and second MOSFET transistors 34 and 36 areturned off until the key fob is activated again by the driver. As aback-up, a manual switch may be provided on the fuse block or elsewherein the car to enable the controller 18 to reactivate the car circuits inthe event that the key fob is lost or inoperative.

The present invention has been described with reference to specificvoltage levels and time periods. A skilled artisan will appreciate thatthese values are a function of the particular battery powered circuit towhich the invention is being applied and by no means are they the onlyvoltage levels and time periods which can be employed.

We claim:
 1. A battery system for use in a vehicle having an electric motor for starting an engine, an alternator driven by the engine to generate electricity, and accessory electrical loads comprising: a first battery for selectively powering the motor to start the engine, and having a first voltage level and a charge level; a second battery to operate and maintain the accessory electrical loads, and having a second voltage level; a charging switch connecting the first battery to the alternator; a charge maintenance device connecting the first battery to the second battery to maintain the charge level of the first battery to a predefined magnitude in response to a control signal; a controller coupled to both the first battery and the second battery to monitor the first voltage level and the second voltage level, and operating the charging switch and the charge maintenance device in response to the first voltage level and the second voltage level.
 2. The battery system of claim 1 wherein the controller produces the control signal thereby activating the charge maintenance device when the first battery requires charging while the alternator is not substantially generating electricity.
 3. The battery system of claim 1 wherein the controller closes the charging switch in response to the second charge level being greater than a first threshold, and opens the charging switch in response to the second charge level being less than a second threshold.
 4. The battery system of claim 3 wherein the second threshold is less than the first threshold.
 5. The battery system of claim 1 further comprising a power switch which connects the accessory electrical loads to the first battery and which is connected to the controller, wherein the controller operates the power switch in response to the second charge level.
 6. The battery system of claim 1 further comprising a power switch which connects the accessory electrical loads to the first battery and which is connected to the controller, wherein the controller operates the power switch to disconnect accessory electrical loads when the second charge level is below a given threshold.
 7. The battery system of claim 1 wherein the charge maintenance device responds to the control signal by applying a series of current pulses to recharge the first battery.
 8. The battery system of claim 1 wherein the charge maintenance device comprises a charge pump.
 9. The battery system of claim 1 further comprising a receiver for sending a signal to the controller to disengage the power switch.
 10. A battery system for use in a vehicle having an electric motor for starting an engine, an alternator driven by the engine to generate electricity, and accessory electrical loads comprising: a first battery for selectively powering the electric motor to start the engine, and having a first charge level; a second battery to operate and maintain the accessory electrical loads, and having a second charge level; means for maintaining a charge of the first battery at a predefined level; means for operating the means for maintaining a charge of the first battery at the predefined level in response to the first charge level.
 11. The battery system of claim 10 wherein the means for maintaining a charge of the first battery at the predefined level connects the first battery to the second battery.
 12. The battery system of claim 11 wherein the means for maintaining the charge of the first battery at the predefined level comprises a charge maintenance device.
 13. The battery system of claim 12 wherein the means for maintaining a charge comprises a controller coupled to the first battery.
 14. The battery system of claim 13 wherein the controller is configured to enable the charge maintenance device in response to the first charge level being less than a first threshold, and is configured to disable the charge maintenance device in response to the first charge level being greater than a second threshold greater than the first threshold.
 15. A battery system for use in a vehicle having a motor for starting an engine, an alternator driven by the engine to generate electricity, and accessory electrical loads comprising: a first battery for selectively powering the motor to start the engine, and having a first charge level; a second battery to operate and maintain the accessory electrical loads, and having a second charge level; a charge maintenance system configured to maintain a charge of the first battery at a predefined level; and a controller coupled to the first battery to monitor the first charge level, and operating the charge maintenance system in response to the first charge level.
 16. The battery system of claim 15 wherein the charge maintenance system couples the first battery to the second battery.
 17. The battery system of claim 15 wherein the second battery includes a glass mat.
 18. The battery system of claim 16 wherein the second battery has a relatively high reserve capacity and is adapted to provide a relatively low-rate discharge for an extended period.
 19. The battery system of claim 16 wherein the controller is configured to activate the charge maintenance system when the first battery requires charging while the alternator is not substantially generating electricity.
 20. The battery system of claim 16 further comprising a charging switch coupling the first battery to the alternator and being coupled to the controller.
 21. The battery system of claim 20 wherein the controller is configured to operate the charging switch in response to voltage across the second battery.
 22. The battery system of claim 21 wherein the controller is configured to close the charging switch in response to the voltage across the second battery being greater than a first threshold, and configured to open the charging switch in response to the voltage across the second battery being less than a second threshold.
 23. The battery system of claim 22 wherein the second threshold is less than the first threshold.
 24. The battery system of claim 16 further comprising a power switch which couples the accessory electrical loads to one of the first battery and the second battery, and which is coupled to the controller.
 25. The battery system of claim 24 wherein the controller is configured to operate the power switch in response to voltage across the second battery.
 26. The battery system of claim 25 further comprising a power switch which couples the accessory electrical loads to the first battery, and which is coupled to the controller.
 27. The battery system of claim 26 wherein the controller is configured to operate the power switch to disconnect the accessory electrical loads when voltage across the second battery is below a given threshold.
 28. The battery system of claim 16 wherein the charge maintenance system is configured to respond to a control signal from the controller by applying a series of current pulses to recharge the first battery.
 29. The battery system of claim 16 wherein the charge maintenance system comprises a charge pump.
 30. The battery system of claim 16 further comprising a charging switch in a first circuit path between the first battery and the second battery and the alternator, the charging switch coupling the first battery to the second battery and the alternator.
 31. The battery system of claim 16 wherein the controller is coupled to the second battery to monitor the second charge level.
 32. The battery system of claim 31 wherein the controller is configured to enable and disable the charge pump in response to the first charge level.
 33. The battery system of claim 32 wherein the controller is configured to open and close the charging switch in response to the second charge level.
 34. The battery system of claim 16 wherein the controller is configured to enable the charge pump in response to the first charge level being less than a first threshold, and configured to disable the charge pump in response to the first charge level being greater than a second threshold greater than the first threshold.
 35. A charge management system for a vehicle comprising: a first battery having a first charge for powering a vehicle ignition system; a second battery having a second charge for powering at least one electrical accessory; a charge maintenance system coupled to the first battery and the second battery and configured to: (a) monitor at least one of the first charge of the first battery and the second charge of the second battery; (b) maintain the first charge of the first battery at a predetermined value by selectively coupling the first battery to the second battery; and (c) disconnect the second battery from the accessory when the second charge of the second battery is at a predetermined value.
 36. The charge management system of claim 34 wherein the charge maintenance system couples the first battery to the second battery until the first charge of the first battery reaches a predetermined value.
 37. The charge management system of claim 36 wherein the predetermined value of the first charge of the first battery is greater than about 13V.
 38. The charge management system of claim 36 wherein the charge maintenance system couples the first battery to the second battery for a predetermined time.
 39. The charge management system of claim 38 wherein the predetermined time for coupling the first battery to the second battery is less than about 24 hours.
 40. The charge management system of claim 36 wherein the charge maintenance system disconnects the second battery from the accessory when the second charge of the second battery is less than about 12.2V.
 41. The charge management system of claim 36 wherein the charge maintenance system comprises a transistor for disconnecting the accessory from the second battery.
 42. The charge management system of claim 41 wherein the charge maintenance system comprises a MOSFET for disconnecting the accessory from the second battery.
 43. The charge management system of claim 36 wherein the charge maintenance system disconnects the accessory from the first battery when first charge is less than a predetermined value.
 44. The charge management system of claim 36 wherein the first battery is a starting battery and the second battery is a reserve battery.
 45. The charge management system of claim 44 wherein the second battery is an absorptive glass mat battery.
 46. The charge management system of claim 44 wherein at least one of the first battery and the second battery is a capacitor.
 47. The charge management system of claim 44 wherein the charge maintenance system comprises a control system.
 48. The charge management system of claim 47 wherein the charge maintenance system further comprises a controller.
 49. The charge management system of claim 48 wherein the charge maintenance system further comprises a computer for executing a control program.
 50. The charge management system of claim 48 wherein the charge maintenance system is under the control of the control program.
 51. The charge management system of claim 50 wherein the charge maintenance system comprises a charge pump.
 52. The charge management system of claim 50 wherein the charge maintenance system comprises a charge maintenance device.
 53. The charge management system of claim 50 wherein the accessory comprises an interior light.
 54. The charge management system of claim 53 further comprising an input device for selectively disconnecting and reconnecting the first battery with the ignition system. 